1. Try to provide an environment that is as stable as possible, fluctuations in the aquarium can have a negative impact on the aquarium. Try to keep the temperature and PH levels fairly balanced in your aquarium.
2. You should always research the different types of fish you are going to be housing together. Certain fish can be extremely aggressive and cannot be paired with other fish of different temperaments.
3. It is generally recommended to use natural gravel for the aquarium. Colored gravel can be used, as long as it is professionally made, certain cheaply made color gravels can be toxic to fish in your aquarium.